Sole for a shoe, in particular for a running shoe

ABSTRACT

A shoe sole includes a midsole and an outsole having discrete outsole elements. The midsole has on the side facing the outsole a multiple of flex grooves crossing each other and creating pads in the midsole. A curved forefoot flex groove emanates from the medial side of the arc and essentially follows a path over one or more of the cuneiform bones and continues between the third and fourth metatarsal phalanges, over the third proximal phalange and continues between the first and second metatarsal phalanges in a direction towards the heel. Both the outsole elements and the pads are arranged to follow an essentially spiral curve around the curved forefoot flex groove. The sole reduces the risk of injury during running, and gives the foot increased compensation possibilities for correcting imbalances especially after heel strike.

The invention concerns a sole for a shoe, in particular for a runningshoe. One type of running shoes of the state of the art has in commonthe concept of protection of the foot. More precisely, the shoe isconsidered a sheltering instrument for the foot. This protection concepthas lead to relatively heavy running shoes, which often have a sole orinsole with a high degree of cushioning in order to mitigate the forcereactions stemming from the heel strike and acting on the ankle jointand the leg. Another type of running shoes are ultra lightweight shoeswhich often are below 300 grams. This type is minimalist having thinsoles and thin uppers. When designing shoes, the shoe industry has for along period had the natural moving foot as the ideal state of motion,e.g. barefoot running on grass, where the foot unconstrained by a shoeis allowed to perform its natural motion. However, once the shoe is onthe foot, natural motion of the foot is impeded. As an example, theangle of the metatarsal phalangeal joint is reduced considerably whenwearing shoes. The metatarsal joint angle is the angle between theground and the metatarsal phalanges. If measured at the instant justbefore pushing off from the ground, this angle is in barefoot runningclose to 60 degrees and in so called technical or athletic running,where running shoes are used, reduced to only 35 degrees. Impediment ofthe natural motion of the foot means among other things that the musclesof the leg and foot which are active during barefoot running are alsoconstrained. These muscles are not allowed to act with their fullstrength, and thus the shoe, if wrongly designed, will limit the abilityof the runner to move efficiently. His performance is lowered ascompared to barefoot running. Some of the key muscles during walking andrunning are musculus flexor hallucis longus and musculus extensorhallucis longus. The importance of these strong muscles when consideringbarefoot running in relation to running with shoes has already beenacknowledged in U.S. Pat. No. 5,384,973, which is incorporated herein byreference. More specifically U.S. Pat. No. 5,384,973 describes a midsolefor a running shoe which sole has a multiple of flex joints or groovesin longitudinal and transversal direction. A number of discrete outsoleelements are connected to the midsole. This structure allows the toes ofthe foot to act independently and to increase the stability of the shoe.In particular, the flex joints have created an isolated sole area forthe hallux, hereby allowing flexor hallucis and extensor hallucis longusto play a greater role during running. U.S. Pat. No. 5,384,973 describesthe relatively thick midsole of current running shoes as a reason forinstability leading to risk of injuries. In order to reduce this risk,U.S. Pat. No. 5,384,973 provides as already described a solution withflex joint grooves in the sole and particularly along the hallux betweenthe first and second toe. This prior art solution is an improvement overearlier prior art, in that injuries from running can be lowered.However, the solution in U.S. Pat. No. 5,384,973 is essentially directedtowards a running shoe for sprinters who are during a sprint mostlyrunning on the forefoot. Marathon runners, on the other hand run slowerand use a greater area of the foot.

WO99/05928 describes a skateboard shoe which has a midsole which on theside facing the outsole comprises a multiple of flex grooves crossingeach other and creates pads in the midsole. The midsole further has acurved channel which emanates from the medial side of the arch andessentially follows a path over one or more of the cuneiform bones ofthe foot of a wearer, and continues between the third and fourthmetatarsal phalanges up to approximately the toe end. Although this shoeis not directed towards running, the design of the forefoot in themidsole has flexing characteristics, which could be of advantage torunners. Modifications are needed, though, because the concrete designof the outsole adds weight and constrains some of the flexibilityachieved with the midsole.

In the light of the foregoing, the present invention sets out to solvethe problem of how to reduce further the risk of injury during running.

This is achieved with a sole according to claim 1.

The invention takes its offset in the basic assumption that naturalrunning is the ideal situation, and that a sole should be designed in away that brings running as close to the ideal situation as possible.Instead of extensive cushioning in running shoes, or extreme reductionof the weight, a concept of supporting the foot in its natural motionduring running has been developed.

Thus, the inventive sole is characterized in that the outsole consistsof discrete outsole elements, and that the pads in the midsole as wellas the discrete outsole elements are arranged to follow an essentiallyspiral curve around a curved forefoot flex groove. This curved flexgroove enables the sole to bend in the longitudinal direction along abending line between the first three metatarsal phalanges on the onehand, and the lateral two metatarsal phalanges on the other hand. Theimportance of this line of flexibility and the existence of this “2-3split” has in the eyes of the applicant not been correctly addressed inmodern sole design, particularly in soles for running shoes. Recognizingthis bending line in the sole design by allowing the sole to be bentalong this axis enables the supinating and pronating muscles of the legto compensate faster after heel strike in the situation where the footeither pronates or supinates. The optimum flexibility has been achievedby letting each discrete outsole element correspond to an isolated padof the midsole. This enables the midsole pads to act more independentlyfrom each other during running dynamics. Thus, in the case of a toolarge pronation, i.e. the case where the arch of the foot is moved tothe medial side, the supinating muscle flexor hallucis longus willcounteract the pronation by a supinating reaction on the medial side ofthe foot. This supinating counteraction is made in order to get theankle into neutral position where no supination or pronation exists.Counteraction will be faster with a sole having the inventive curvedflex groove and independent midsole pads and discrete outsole elements,because muscle flexor hallucis does not have to “lift” the whole sole inorder to counteract, but only a part of it, namely the part on themedial side of the curved flex groove, i.e. the part which comprises thefirst, second and third metatarsal phalanges. As the inventive solegives the foot increased compensation possibilities for correctingimbalances especially after heel strike it contributes to a fasterequalization of the ankle position also in the cases of large pronationor supination and the risk of damage to the ankle in these situations isreduced. In the end, the risk of running injuries is reduced.

In order to support the concept of getting close to natural running,extensive data had to be collected and turned into practical measures.The last used for the inventive sole is a so called anatomical lastwhich means that is has a higher degree of similarity to the footcompared to a normal foot shaped last. In other words, the anatomicallast is in shape very close to the human foot. The high degree ofsimilarity has been achieved by measuring 2200 feet. By examination ofthe many data from the feet we have created so to speak “an averagehuman foot” and put this shape into the last. During manufacturing ofthe shoe, the sole material, which is injected, will follow the shape ofthe anatomical last and hereby take the shape of the average human foot.The foot sole will rest comfortably on the manufactured sole, becausethe sole is a mirror of the foot sole.

In a preferred embodiment, the curved forefoot flex groove is continuedfrom the start of the proximal metatarsal phalanges over the thirdproximal phalanges, crossing the second and continued in a directionbetween the first and second metatarsal phalanges in a direction towardsthe heel. This measure further increases the longitudinal flexibility ofthe sole.

A transversal flex groove is made in the midsole from the medial sidetowards the lateral side in the region where the metatarsal phalangesmeet the proximal phalanges. This flex groove is essentially a straightgroove, is crossing the curved forefoot flex groove, and addsflexibility in the transversal plane of the sole. This groove ispreferably made wider than other flex grooves in the midsole because itexerts influence on the metatarsal phalangeal joint angle.

A further flex groove follows the joints between the proximal phalangesand the medial phalanges.

The curved forefoot flex groove emanates from the medial side of thearch, and has a straight portion which runs parallel to a reinforcementbar made in the midsole. The reinforcement bar adds strength to themidsole, and is connected to a midsole pad in the medial heel area,which pad when equipped with a discrete outsole element is flush withthe ground. This design counteracts over-pronation.

Preferably, the heel portion of the midsole also has a curved flexgroove emanating from the medial side and stretching to the lateralside. This flex groove is deeper and wider than the transverse flexgrooves in the forefoot, and has the function of decoupling the heel ofthe sole from the forefoot sole in order to allow “horizontal flex”,i.e. in order to allow horizontal movement of the heel portionespecially during heel strike. This functionality can be compared to thehuman fat padding in the heel area; it also allows a small horizontalmovement back and forth. In copying this feature from nature, a shoewith the inventive sole allows a runner to get closer to naturalrunning.

Preferably, a second curved heel flex groove is made in the heel. Thisflex groove delimits the flat, horizontal portion of a heel pad from atapered heel pad, and enables the tapered heel pad independent movement.

The curved forefoot flex groove and the curved heel flex groove arepreferably devoid of any outsole material in order to allow asunconstrained movement of the foot as possible.

The subclaims specify further advantageous designs of the sole.

The invention is now described in detail by way of the drawings in which

FIG. 1a is a split view of the inventive sole with a midsole and a shank

FIG. 1b is a cut away view of the sole of FIG. 1a along an axis A-A

FIG. 2a is a split view of another inventive sole with a midsole and ashank

FIG. 2b is a cut away view of the sole of FIG. 2a along an axis A-A

FIG. 3a shows the shank used in a perspective view

FIG. 3b shows the shank of FIG. 3a in a side view

FIG. 3c shows the shank of FIG. 3a in a rear view

FIG. 4 is a view of a first embodiment of the bottom of a midsole usedin the invention

FIG. 5 is a drawing showing the bones of the medial side of the foot

FIG. 6 shows the right human foot as seen from below

FIG. 7 is a second embodiment of the bottom of a midsole with an outsoleaccording to the invention

FIG. 8 is a third embodiment of the bottom of a midsole with an outsoleaccording to the invention

FIG. 9 is a fourth embodiment of the bottom of a midsole with an outsoleaccording to the invention

FIG. 10 is a view of the lateral side of the midsole used in theinvention

FIG. 11 is a view of the medial side of the midsole used in theinvention

FIG. 12 is a view of the medial side of an alternative midsole used inthe invention

FIG. 13 is a view of the lateral side of an alternative midsole used inthe invention

FIG. 14 is a view of a first heel embodiment of the midsole used in theinvention

FIG. 15 is a view of a second heel embodiment of the midsole used in theinvention

FIG. 1a is a perspective view of the sole 7. In a preferred embodiment,the sole consists of three layers, namely as first layer a midsole 1, asecond intermediate layer 2, and a third layer 3 constituting theoutsole. A shank 4 is placed on top of the midsole. FIG. 1b shows thesole in a longitudinal cut along the axis A-A of FIG. 1a . For reasonsof clarity, the medial support structure has been cut away in the viewof FIG. 1a but it can be seen as reference numeral 158 in FIG. 11.

Midsole 1 is in the preferred embodiment made of light polyurethane (PU)material, also called PU light. This material is a known special variantof PU which has a low density (0.35 g/cm³), i.e. is a lightweightmaterial. A further characteristic is a good return of energy absorbedfrom the runner, which characteristic is of importance for long distancerunning. Shore A hardness is between 38 and 40. Alternatively, alsoethylene vinyl acetate (EVA) can be used as midsole because it has alower specific gravity than PU light resulting in a lighter sole.However, EVA tends to quick ageing under frequent force influence fromthe foot. This ageing is seen as wrinkles in the material. It is notform stable, and after a while it is compressed and does not return toits original shape.

Midsole 1 is in this preferred embodiment covered with the secondintermediate layer 2 which has the same profile as the midsole. FIG. 1bshows this profile and the second layer 2 is so to speak a replica ofthe bottom of the midsole 1. Layer 2 has the function of a protectivelayer, consists of thermoplastic polyurethane (TPU), and is anintermediate layer which is thin, typically 0.5-2 millimetres. It has ashoe A value of 65 plus/minus 3.

The third layer 3 is the outsole, which consists of a number of discreteoutsole elements (e.g. reference numbers 120-123 in FIG. 8), whichtogether add up to be the outsole. Under the term “discrete outsoleelement” is understood a piece of outsole that is not cast or moulded inthe same process as the midsole or the intermediate layer 2, but isadded or bonded to e.g. layer 2 later. Further, a discrete outsoleelement is not connected to the other outsole elements. In more detail,the outsole 3 consists of a plurality of outsole elements which can beperceived as islands that are not interconnected, separated by one ormore grooves in the midsole. The elements are preferably made of rubber.Instead of rubber, TPU can be used as material for the discrete outsoleelements, but the gripping characteristics of TPU are inferior comparedto rubber. The rubber used is a conventional Nitril Butadine Rubber(NBR), which is preferred for running shoes because of its relative lowweight. It has a shoe A value of 55 plus/minus 3. For other types ofshoes, latex (comprised of a mixture of natural and synthetic rubber)can be used. The outsole elements are spaced apart with grooves 5, 6 inthe intermediate TPU layer 2 and in the midsole 1, and are placed onprotrusions or pads 10, 11, 12, 13 (FIG. 1b ) made in the intermediateTPU layer. The pads and grooves of the intermediate layer mate with thecorresponding pads and grooves of the midsole.

FIG. 2a shows another sole, which has a midsole 1 with lateral andmedial support structures, and a shank 4 amended as compared to theshank in FIGS. 1a and 1b . FIG. 2b shows the sole of FIG. 2a in a cutaway view. The reference numerals of FIGS. 1a and 1b are the same inFIGS. 2a and 2 b.

Manufacturing of the sole 7 consisting of the sole parts 1, 2 and 3. ismade in the following way. In a first step, the TPU intermediate layer 2and the outsole elements 3 are produced in a separate manufacturingprocess to become an integrated entity. In a second step, the midsole 1is connected to the integrated entity consisting of layer 2 and outsole3. Step one and step two will now be described.

In step one, the TPU intermediate layer 2 and the discrete outsoleelements 3 are manufactured to become an integrated entity. First thediscrete outsole elements are manufactured in a rubber vulcanisationprocess. Then the outsole elements are placed in a mould, where TPU isinserted above the elements. The mould is closed, and under applicationof heat and pressure the TPU is shaped into the desired shape. After acuring time, the integrated entity of outsole elements and TPUintermediate layer is finished. Although the TPU layer is manufacturedin a casting process, alternative manufacturing processes are availablefor producing the second layer 2. Thus, the TPU can be injection mouldedin a known manner, or the TPU can be a foil-like raw material like asheet placed above the outsole elements 3 before joining these elementsand the TPU using heat and pressure.

Bonding between the TPU intermediate layer 2 and the outsole elements 3are made with glue which is activated by the heat during moulding theTPU onto the outsole elements. A simple adhesion without glue betweenTPU and rubber during the moulding process proved not durable. Beforeadding glue between TPU intermediate layer 2 and outsole elements 3, therubber surface of the outsole elements 3 must be halogenated in aprocess which removes fat from the rubber and thus enhances theadhesion.

In step two of the manufacturing of sole 7, the midsole 1 is unifiedwith the integrated entity consisting of layer 2 and outsole elements 3from step one, as well as with a shoe upper. More specifically, the TPUintermediate layer 2 with the outsole elements 3 is placed in aninjection mould together with the shoe upper, after which PU is injectedinto the mould and bonds to the shoe upper and the integrated entityconsisting of layer 2 and outsole elements 3. The PU thus bonds to theside of the TPU intermediate layer 2 which is closest to the human foot.After this second step, sole elements 1, 2 and 3 have become integratedinto one entity. Preferably, shank 4 is only partly embedded in PUduring the injection process.

The TPU intermediate layer 2 has a double function in that it lowers thebreakability of the midsole and reduces the cycle time on the PUinjection machinery. This will be detailed in the following.

In principle, the TPU intermediate layer can be omitted, and theisolated outsole elements placed directly in the mould by the humanoperator before PU injection. This would however cost processing time onthe PU injection machine, because placement of the many discrete outsoleelements takes time. Instead, by manufacturing the TPU intermediatelayer 2 and outsole elements 3 in a separate process as described above,the PU injection machine is free to manufacture midsoles most of thetime. Machine waiting time is reduced. However, the use of the TPUintermediate layer has a further advantage, namely reducing a tendencyof the PU light midsole to break. If the discrete outsole elements 3 areplaced directly against the PU light midsole without any intermediatelayer 2, the midsole tends to break in durability tests due to thehigher number of flex grooves. Such breakage will allow water to enterthe shoe during wear. The reason is that when injecting PU into themould during manufacturing, air bubbles tend to occur in the midsole.The bubbles occur because the PU is not able to press out air aroundsharp edges in the channels of the mould. This is probably due to thelow specific gravity of the PU. The result is that air bubbles arecontained in the midsole, thus making the sole liable to penetration ofwater when the midsole breaks or experiences cracks. TPU has a largerspecific gravity, and does not cause problems with trapped air bubblesduring manufacture. In other words, the midsole 1 is not liable to waterpenetration caused by air bubbles and breakage due to protection by theintermediate layer 2, which contributes to keeping the interior of theshoe dry.

As material for midsole 1 PU has been chosen over TPU. In principle, thewhole midsole could be made of TPU, but PU light has a lower specificgravity thus lowering the weight of the shoe. Further, PU has good shockabsorbing characteristic which is important especially for runningshoes.

Between the midsole 1 and an insole (not shown on the figures) is theshank 4 (FIGS. 3a to 3c ), which consists of a mixture of thermoplasticpolyethylene (TPE) and nylon and is partly flexible. It extends from theheel portion to the toes, and has in the heel portion preferably anopening 8, where the polyurethane used for the midsole 1 enters duringthe injection process. This feature improves the shock absorption in theheel. In the front end, the shank has two curved fingers 15 and 16extending under a curvature in the longitudinal direction, and a smallfinger 14 in the middle. These fingers support in particular the first,fourth and fifth metatarsal phalanges. It has been found that two tothree fingers suffice instead of having one supporting finger for eachray in the foot. The shank is designed to be “anatomical”, i.e. itfollows the average foot more closely than conventional shanks. Theshank is manufactured in an injection process, and is made bendable inthe transversal direction just where the fingers of the shank starts,corresponding to the proximal end of the first, fourth and fifthmetatarsal phalanges, see the line indicated by reference number 18 inFIGS. 1a, 2a and 3a . Thus, the shank is bendable in a directionorthogonal to the longitudinal axis of the sole. The bend ability isachieved in a process during manufacturing of the shank, wherethermoplastic polyethylene is injected from the heel end and nylon fromthe toe end. The two compositions meet at the bending line and the soleis bendable from this line 18 because polyester is soft compared to hardglass fibre. As a further measure, the shank is also flexible in itslongitudinal direction along a line 19 (FIGS. 1a and 2a ), because theshank should preferably be more flexible on the lateral side than on themedial side. With this measure, the torsional stiffness in thelongitudinal direction is adjustable. FIG. 3a shows the small finger 14.Tests have shown that pushing off in the forefoot during running isimproved by increasing the stiffness in this area of the foot.

Preferably, the shank 4 is placed on top of the midsole. Alternativelyit could have been placed between the midsole 1 and the intermediatelayer 2, but this placement would lead to friction problems between thehuman heel and the heel of the midsole. During running, the midsolewould compress and decompress in the heel area, each compressionallowing the human heel a movement downwards, and each decompressionallowing the human heel to move upwards. Repeated movements downwardsand upwards against the heel creates friction and discomfort for therunner. Instead, by placing the shank on top of the midsole, friction islowered because the shank as an early stiffening layer reduces thelength of downwards and upwards movements.

In one embodiment, the shank is integrated in the strobel sole, which isa flexible sole connected and typically sewn to the upper (not shown inthe figures). The strobel sole is often a textile. The integration ofthe shank into the strobel sole gives a harder sole because the strobelsole contributes to the hardness. This embodiment has the advantage ofan easier manufacturing, because the shank is sewn into the strobel soleand does not have to be placed in the mould before PU injection asdescribed above. In the preferred embodiment however, the shank is gluedto the strobel sole, which together with the upper is mounted on thelast. The last is placed in the mould which is closed, after which PU isinjected into the mould.

The shank 4 has an offset heel area 25 as shown in FIG. 3a . This offsetheel area defines a cavity 17 for receipt of PU or other material. Theoffset heel area functions as a platform for the PU entering theessentially elliptically shaped opening 8. The cavity is made by a rimin the shank, which rim follows around the opening 8. The rim is slopinginwardly towards the centre of the opening, hereby defining the cavity17. In one embodiment of the invention, the PU fully fills the cavity,which, when taken at the centre of the opening, gives the followinglayering in the heel area from top to outsole: strobel sole, PU, TPUintermediate layer 2 and outsole 3. In the arch area of the solehowever, the order of the layers is: strobel sole, PU, shank 4, PU, andTPU intermediate layer 2. As there is no shank material in the opening 8of the heel, this area is more flexible.

In order to lower the hardness in the heel area even further, a comfortelement 9 (FIGS. 2a and 2b ) can be placed in the cavity. In thisembodiment, the PU only fills the opening 8 of the shank. Such comfortelements are well known and commercially available. The comfort elementis 9 millimetres in height, the PU midsole below is 8 millimetres, theTPU intermediate layer 1 millimetre and the discrete rubber outsole 3 is2 millimetres. The ratio between the height of the comfort element andthe PU midsole below can be varied in a wide range, but should notexceed 1.5:1. Otherwise, the design would approach the conventionalcushioning techniques, which as already described has drawbacks.Advantageously, the PU bonds to the comfort element, hereby ensuring afixation of the material without any further manufacturing steps.

Referring to FIG. 3b , a transition zone 39 in the shank between thearch area and the heel area should preferably not make an angle β ofmore than 50 degrees with the horizontal plane of the offset heel area.A larger angle provides discomfort to the runner due to a sharp edge.Advantageous angles are around 30 degrees. FIG. 3c shows the shank in arear view. The transition zone 39 not only slopes from the arch areatowards the heel area, but also from the medial side of the shank to thelateral side. In this way the shank is raised to give support to thearch of the foot.

The shank 4 is in both embodiments (i.e. cavity fully or partly filledwith PU) fully or partly embedded in the PU midsole. In the forefoot andin the arch area, the shank is placed close to the strobel sole, eitherwith or without PU in between strobel sole and shank. In the offset heelarea the shank is placed close to the outsole.

Thus, by offsetting the longitudinally extending shank in the heel areaof the sole, a cavity in the heel zone is created. This offset heel areahas a platform on which the PU from the midsole is embedded during theinjection process. The PU enters the cavity through a hole made in theplatform, or, more precisely, through an opening made in the offset heelarea of the shank. The heel area is offset towards the outsole to asecond horizontal plane different from a first horizontal plane of thearch area of the shank. Our tests have shown, that this design gives abetter running experience because the heel area of the sole has becomesofter.

A special insole has been provided. The insole consists of two layers.The upper layer is a polyester material, which is lightweight, andbreathable. The bottom layer is made in two versions. For class Arunners the bottom layer consists of EVA, which advantageously has a lowweight, and for class B runners the bottom layer is made of PU foam.This is a more expensive solution, but gives a better insole. The bottomlayer has through-going holes for breathing. In the heel portion of theinsole an area with shock absorbing material is placed, and in theforefoot area of the insole an energy return material is placed whichduring push off releases most of the energy received during heel strikeand full foot contact. Instead of placing the shock absorbing materialin the insole it can also be embedded during the injection process inthe heel of the midsole 1.

The inventive midsole 1 is shown in FIG. 4 with a direct view from thebottom. The midsole has a forefoot portion 23, a top end 22, a lowerheel portion 20, an arch portion 21 and a lateral side portion 24. Fourflex grooves 27, 29, 31 and 34 traverse the forefoot 23. The grooveshave a depth of approximately 50-60% of the thickness of the forefootmidsole, in this example 3-4 millimetres. A curved flex groove 63extends from the medial side 49 of the arch portion 21 and continuesalong portions 48, 32, 59, 60 and 61. The flex grooves createprotrusions or pads 26, 28, 30, 33, 35, 38, 40, 46, 50, 52, 54, 56, 62which in shape correspond to the shape of the discrete outsole elements3 but have a larger area. Thus, the pads are closer to each other thanthe discrete outsole elements mounted on the TPU intermediate layer 2.As will be described later, this has shown to have a positive effect onslip resistance. Pads 33 and 35 are extended in the lateral horizontaldirection to become the most extreme points on the lateral side of thesole. When outsole elements are placed on the pads, this extension willcontribute to stabilizing especially when the foot supinates. Areinforcement bar 47 runs slanted from the medial side to the lateralside. The reinforcement bar is part of the midsole and made during theinjection process. It is thicker than the midsole on the lateral portion37 and on the medial portion 49, and adds stiffness to the midsole. Itruns parallel with the shank 4 (not visible on FIG. 4) which is placedon the other side of the midsole, i.e. the side facing the foot.

The curved flex groove is substantially wider than the other flexgrooves. In one embodiment it is six millimetres wide, the flex groove34 three millimetres and the flex groove 31 four millimetres. As a rule,the curved flex groove is between 1.5 and 3 times wider than the otherflex grooves. The width of the curved flex groove can be varied, but ithas preferably a width corresponding to 1-2 times the distance betweenthe third and fourth metatarsal phalanges. However, the distance may notbe too wide because this would cause too much flexibility. Further, theflex groove has essentially a constant width along its curve in theforefoot.

The curved flex groove 63 intersects the transverse flex grooves 29, 31and 34. The curved flex groove thus runs in longitudinal direction fromthe medial side of the arch to an apex point 59 in the metatarsal zoneof the foot. From this apex point the groove continues in the oppositedirection along path 60 and crossing flex grooves 57 and 55. It endsapproximately under the ball of the big toe in flex groove 61. Thecurvature of the groove in essence gives the sequence of midsole pads aspiral shaped character: Thus, starting in an origo point O in pad 62, acurve 64 can be drawn which describes a somewhat compressed or eccentricspiral graph. When mounted later in the manufacturing process, thediscrete outsole elements 3 will describe the same curve.

The function of the curved flex groove 63 is to enable natural runningby giving the midsole a bending line in longitudinal direction betweenthe third and the fourth metatarsal phalanges and hereby giving thecharacteristic “2-3 split” of the rays of the foot attention. This willbe detailed in the following. FIG. 5 shows the bones of a right footfrom the medial side with first metatarsal phalange 85, calcaneus 69,the tuberosity 68 and the superior tuberosity 67. FIG. 6 shows a righthuman foot from below. Reference number 70 describes the talus, 71 thenavicular bone, and 72, 73 and 74 the three cuneiform bones, i.e. themedial, the intermediate and the lateral cuneiform bone respectively.Line 89 represents a folding line in the human foot between cuboid bone87 on the one hand, and the lateral cuneiform bone 74 and the navicularbone 71 on the other. The foot is flexible and bendable along thisfolding line meaning that if bending is made along a longitudinal axisrunning between the fourth metatarsal phalanges 82 and the thirdmetatarsal phalanges 83, the three most medial phalanges (83, 84, 85)will bend to one side, and the two most lateral phalanges (81, 82) willbend to the other side. Recognizing this bending line by allowing thesole to be bent along this axis enable the supinating and pronatingmuscles to compensate faster after heel strike in the situation wherethe foot either pronates or supinates. Thus, in the case of a too largepronation, i.e. the case where the arch of the foot is moved to themedial side, the supinating muscle flexor hallucis longus willcounteract by a plantar flexing reaction on the medial side of the foot.According to the invention, counteraction will be faster with a solehaving a curved flex groove and independent midsole pads and discreteoutsole elements because musculus flexor hallucis does not have to“lift” the whole sole, but only a part of it, namely the part on themedial side of the curved flex groove, i.e. the part which comprises thefirst, second and third metatarsal phalanges. This supinatingcounteraction happens in order to get the ankle into neutral positionwhere ideally no supination or pronation exists.

The outline of the curved flex groove 63 is shown with the line 90 inFIG. 6. This line shows where the curved flex groove is placed in themidsole 1. Note that the flex groove 63 is placed on the side of themidsole facing the outsole. Curved flex groove 63, represented by line90 in FIG. 6, emanates from the medial side of the arch and starts underthe navicular bone 71. Alternatively the medial cuneiform bone 72. Itcrosses the lateral cuneiform bone 74 and continues between the thirdand fourth metatarsal phalanges up to the beginning of the jointsbetween the metatarsal and proximal phalanges (75, 76, 77, 78, 79).These joints are shown by line 92, which also represents flex groove 31in FIG. 4. The curvature of line 90 (i.e. groove 63) in the region ofthe cuneiform bones can be changed. Also the starting point of the curveon the medial side can be raised towards the toe end or lowered towardsthe heel.

Turning back to FIG. 4, an ideal landing point A is shown in the lowerheel portion. This point is the optimum point of landing for a runner,and it is placed just below the calcaneus, offset to the lateral side.Real life test shows however that in practice this optimum landing pointcannot be reached. Typically, real life runners touch ground somewherealong the line marked B, reference number 41. The point of landing isdependent on the speed of running, and may even be different from rightfoot to left foot. However, moving the point closer to A results inimproved force and energy consumption, and tests have shown that thepoint of landing with the sole can be moved to approximately C shown inFIG. 4. The basic idea with moving the point of landing as close to A aspossible is the recognition that the muscles in the leg responsible forpropulsion can be activated at an earlier time to become mechanicallyactive—they are earlier in tension and able to create forwardpropulsion. In order to move this landing point as close to A aspossible, two measures have been taken in the design. First, the heightof the heel has been lowered or more specifically, the height of thelower heel portion 20 has been lowered in order to get the human foot asclose as possible to the ground. Compared to state of the art runningshoes, this height can be reduced, because the inventive design does notmake use of extra cushioning materials in the sole. Cushioning is aninherent characteristic of the PU midsole material used. In general,cushioning should not be avoided but kept to a minimum because itabsorbs energy without returning it to the foot. In the preferredembodiment the maximum height or thickness of the midsole in lower heelportion 20 is between eight and twelve millimetres, preferably eightmillimetres. This is the heel spring of the midsole and corresponds tothe thickness of the heel in point A of FIG. 4. The second measure takenin order to move the point of landing closer to A is by designing thelower heel portion 20 of the midsole 1 with a double tapering. FIG. 14shows the rear of the foot 150 wearing a shoe with the inventive midsole1 and discrete outsole element 124. The midsole in the rear foot area isasymmetrical around a vertical line B-B dividing the midsole into twohalves. In the optimum upright standing position, the vertical axis B-Bwould go through the ankle joint and the tibia. The midsole is splitinto a medial heel portion 143 and a lateral heel portion 151. Further,a horizontal line C-C divides the midsole in the rear foot area into thelower heel portion 20 and an upper heel portion 142. The lines B-B andC-C together divides the heel of the midsole into four sections: I, II,III and IV. It is clear from the drawing that none of the four sectionsI-IV are identical. The tapering 141 enables the foot to touch down inpoint C (FIG. 4). As seen in FIG. 14, the tapering is not only insection III, but also partly in section IV. In section IV, i.e. on themedial side of lower heel portion 20, the tapering stops, and becomesaligned with a geometric plane corresponding to the geometric plane ofsurface 149 (FIG. 10). FIG. 10 shows the tapering in more detail, and itwill be understood that the tapering not only runs from the centre ofthe lower heel portion 20 towards the lateral side as depicted in FIG.14, but also from the centre towards the heel end. FIG. 11 shows withreference number 153 that on this point of the medial inner side of theheel, the lower heel portion has full contact with the ground via anoutsole element. Supports 147 are an integral part of the midsole.

On heel strike, the midsole and outsole is designed to allow so calledhorizontal flexing. This is achieved with the curved heel flex groove 45of FIG. 4, which groove is deeper and wider than the transverse flexgrooves in the forefoot, and has the function of decoupling the heel ofthe sole from the forefoot sole in order to allow “horizontal flex”,i.e. in order to allow horizontal movement of the heel portionespecially during heel strike. This functionality can be compared to thehuman fat padding in the heel area which also allows a small horizontalmovement back and forth. A second curved heel flex groove 42 isdecoupling the pad 40 from the pad 38 at heel strike. Preferably, onediscrete outsole element is applied to pad 40 and another element to pad38. Pad 38 and pad 46 are fully horizontal, i.e. when the discreteoutsole elements have been applied, these elements have full groundcontact and are not curved as pad 40. The full ground contact of pad 46is important to reduce the effects of overpronation, i.e. the situationwhere the foot continues pronating during the mid-stance. The doubletapering of pad 40, as already described, is delimited by the secondcurved heel flex groove 42 from where the tapering starts. Also inpoints 43 and 44 pad 40 is tapered.

In FIG. 15 a second embodiment 168 of the heel of the midsole is shown.The lower heel portion 20 is provided with steps 169, 170 and 171. Thesesteps are staggered in relation to each other and made as part of themidsole in PU. The staggered steps 170 and 171 are made in order tostiffen the lower heel portion. Such stiffening effect is provided bydirect injected PU in edge zones. Step 169 which is also shown in FIG.14, clearly extends longer to the lateral side than the rest of themidsole in the heel portion, e.g. as compared to support arm 145, and isprovided to achieve enhanced stability. It will be noted from FIGS. 14and 15 that the medial heel portion 143 essentially can be aligned witha vertical line D, whereas the lateral heel portion 151 is aligned witha slanted line E.

Comparative tests between the inventive running shoe and a state of theart running shoe have been made. 12 male test persons were using theinventive shoes and the state of the art shoes. Using a goniometerplaced on the heel of the persons, foot switches for detecting groundcontact and an accelerometer mounted on the tibia muscle, differentparameters as angles, velocities and accelerations have been measured.Table 1 shows the comparative test results.

TABLE 1 Comparative test State of the art Inventive shoe running shoeRear foot angle at touchdown   −3.4°   −2.8° (negative angle =inversion) Maximal rear foot angle    10.2°    10.1° (positive angle =eversion) Rear foot angle velocity at touchdown   175°/s   340°/sMaximal rear foot angle velocity   390°/s   480°/s Mean rear foot anglevelocity   200°/s   290°/s

The rear foot angle at touchdown was a bit larger than in the state ofthe art shoe. Thus the heel as a mean value was turned 3.4° to thelateral side measured in relation to the ideal zero degree situation.The maximal eversion angle on the other hand was found to be 10.2° ascompared to 10.1° of the state of the art shoe. The maximal eversionangle is the angle measured when the heel of the foot turns to themedial side. Of particular interest are the velocity dynamics duringtouchdown, where the maximal rear foot angle velocity is 390°/s (degreesper second) as compared to 480° Is on the state of the art shoe and themean rear foot angle velocity 200°/s as compared to 290°/s. In the eyesof the applicant this is a significant difference, because the lowermean and maximum velocity results in a more stable shoe. This means thatfrom the instant the heel hits the ground until eversion is finished,the inventive shoe is significantly slower and thus more stable. Theresult is a reduced risk of injuries in the ankle. The low mean rearfoot angle velocity is partly due to the fact that the shoe has a lowheel which advantageously brings the foot very close to the ground.

FIG. 7 shows a second embodiment of a midsole 118 slightly modified incomparison to midsole 1 of FIG. 4. Apart from the modified midsole, FIG.7 departs from FIG. 4 in that the midsole 118 has discrete circularoutsole elements (101, 102, 104, 105,106, 108, 110, 111, 112, 114, 115)mounted on the midsole. Further, FIG. 7 shows the curved flex groove asreference number 103 following a path 119 up to transversal flex line113 and 107. This flex line corresponds to line 92 in FIG. 6. Also inthe embodiment of FIG. 7, an imaginary eccentric spiral curve can bedrawn starting with an origo O (curve not shown) in outsole element 105and continuing via 104, 106, 108, 110, 111, 112, 114 and ending at 115,hereby curving around the curved flex groove 103. Also here, the outsoleelements are discrete. Thus, elements 104, 105 and 106 although bridgedby connection 109, can be made as isolated outsole elements. Elementpair 108, 110 is another discrete outsole element. FIG. 7 shows that thecurved flex groove 103 can stop at the level of flex line 113. This soledesign will also contribute to increased flexibility of the foot andfaster reaction to excessive supination or pronation. In the heelportion a tapered area 117 enables moving the point of landing closer tothe centre of the heel sole. An outsole element 100 is spaced apart froma reinforcement bar 99 by a heel flex groove 116.

Improvements can be reached by further continuing the curved flexgroove. Turning back to FIG. 6, the curved line 90 continues as curvedforefoot line 91 across the third and second proximal phalanges andmakes a U-turn in the direction of the heel. The curve 91 now runs in anopposite direction between the first and second metatarsal phalanges.This trajectory is also the one shown in the midsole of FIG. 4 andcorresponds to the one seen in FIG. 8.

In more detail, FIG. 8 shows a third embodiment of the inventivemidsole, which in the figure has a TPU intermediate layer 2 and discreteoutsole elements (120, 121, 122, 124, 125) fixated. The discrete outsoleelements function as the tread of the shoe. Due to the flex groovesbetween the discrete outsole elements, the total outsole area is smallcompared to conventional outsoles. This has an effect on the slipresistance. The outsole area, which can also be perceived as a contactarea between outsole and ground, has been further minimised by removingmaterial from the central portion of the outsole elements. Morespecifically, the contact area of an outsole element in the elements ofFIG. 8 is the area close to the edge of the element, whereas the centreof the outsole element is either devoid of material or only having asmall contact area. Removing material from the outsole elements has theadvantage of reducing the weight of the shoe, which is of particularinterest in running shoes. Despite this reduction and the small surfacearea, a surprising effect has been seen regarding icy surfaces, becausethe grip of the sole has been improved compared to conventional soles.This is partly due to the material of the sole which is as mentionedrubber, and partly due to the “islandic” structure of the sole. As anexample, the discrete outsole element 125 of FIG. 8 has a first planesurface 126 and a second plane surface 127. The second surface islowered in relation to the first surface and a third surface 128 is inthe same plane as the first. A fourth plane surface 133 constitutes thesurface of the TPU intermediate layer 2, and is lower than planesurfaces 126 and 127. The surface area 133 essentially corresponds tothe surface area of a pad of the midsole (see pad 35 in FIG. 4), albeita bit larger due to the TPU intermediate layer which is covering thepad. As can be seen on FIG. 8, the discrete outsole element 125 covers asmaller area than the corresponding pad in the midsole. This means thatneighbouring discrete outsole elements have a larger distance to eachother than the pads in the midsole as can be seen by comparing thedistance between outsole elements 125 and 123 of FIG. 8. In the currentembodiment, the distance between outsole elements 123 and 125 is fivemillimetres, and the distance between element 122 and 125 tenmillimetres. The relatively large distance between the discrete outsoleelements increases the flexibility of the sole, and has, as alreadydescribed, led to good characteristics on slip resistance. Further, bymaking the area of an outsole element smaller than the correspondingarea of TPU intermediate layer and pad, peeling effects on the outsoleelements can be avoided. They will be less inclined to loosen as thebonding between TPU and rubber is made on a plane surface away fromedges of the surface 133.

The discrete outsole element 125 has sharp edges in an angle of about 90degrees. When walking on an icy surface, the sharp edges penetrate theice which creates a better grip. The total length of the sharp edgesamounts to the sum of the circumference of the discrete outsoleelements. The longer, the better grip one gets. However, with theinvention, the grip has been even further improved. Without being boundby the following theory, it is believed that the flexible discreteoutsole elements allow the foot to react in a natural way in the case ofan icy surface. If you slip on one part of the foot base, the humanbrain will via a muscle action instruct another part of the same footbase to instantly and automatically compensate and try to get a grip onthe ground. Conventional outsoles prevent this compensation because thecompensational muscle reaction is constrained by the normal sole. Adiscrete outsole as in the invention, however, having flexible outsoleislands, allows the discrete action of one or more of the 32 muscles inthe foot. The improved gripping characteristic of the inventive sole wasconfirmed in laboratory tests in comparison with state of the artrunning shoes. Slip resistance showed to be improved both in relation toa wet surface and in relation to an icy surface. An improvement in slipresistance of the embodiment of FIG. 8 can be made by building channels129 into the first surface 126. On wet surfaces, aqua planning can arisebecause water is trapped in the groove of the lower second surface 127.Channels 129 will allow the water to escape, hereby lowering the risk ofaqua planning and increasing the slip resistance even further.

FIG. 9 shows a fourth embodiment of an inventive midsole 135, whichmidsole has a TPU intermediate layer 2 and an alternative tread.Discrete outsole element 130 exhibits undulating channels 131, whichacts as grooves transporting the water away. Typically, grooves of onemillimetre are used. The embodiment in FIG. 9 shows the use of a mixtureof the outsole elements of FIGS. 8 and 9. The discrete outsole element132 in the lower heel portion exhibits undulating channels in adirection slanted to the longitudinal direction of the sole.

FIG. 10 shows in a lateral side view an embodiment of the midsole 135with discrete outsole elements 139 and a TPU intermediate layer 134. Theheel end 137 extends vertically to a top point 152 on the medial side ofthe midsole and to a lower point 140 at the centre of the heel end 137.The top or apex of the upper heel portion is approximately at the samelevel as the instep of the shoe upper, see FIG. 12. The upper heelportion thus extends to the location where the Achilles' tendon is fixedto the calcaneus, and the upper heel portion essentially covers thetuberosity of the calcaneus on the medial and the lateral side. Anopening 144 is made on the lateral side in order to increase flexibilityby lowering the structural support given in this area. However, inprinciple the whole calcaneus can be supported by the verticallyextended midsole material. The heel is extended vertically to a pointessentially corresponding to the superior tuberosity of the calcaneus,see reference number 67 in FIG. 5. A support arm 145 connects the heelend 137 with the lateral heel portion 151, and ensures stability. Byextending the heel of the midsole into an upper heel portion which formsan integrated entity with the midsole (preferably as described injectionmoulded), the heel cap of traditional shoes can be omitted, herebysimplifying the shoe and reducing weight and cost. In an exemplaryembodiment the vertical height measured from the geometric planecorresponding to surface 149 to lower top point 140 is 61 millimetres.With TPU intermediate layer 2 and discrete outsole elements mounted theheight becomes 65 millimetres.

On the lateral side of the midsole 135, a measure is taken to compensatefor the proximal head of the fifth metatarsal phalanges which causes aprotrusion or a local extremity of the foot, also known as tuberositasossis, see reference number 86 in FIG. 6. This head, if encapsulated bya relatively stiff sole material, will be subjected to friction betweenhead and sole material, and will reduce the flexibility of the shoe. Inorder to avoid this friction and to allow the head and the joint freemovement, an opening or window 148 as shown in FIG. 10 is created in themidsole material. Thus, in this area of the midsole, the midsole isdevoid of sole material.

FIG. 11 shows midsole 135 from the medial side with the large supportarea of the medial heel portion 143. As described, top point 152 is inthe area of the superior tuberosity of the calcaneus. From this point,the edge of the midsole of the medial heel portion degrades in adirection towards the toe end along a curve 154 via supporting arm 155to the forefoot. A corresponding support arm is found on the lateralside, reference number 156 (FIG. 10). Thus the midsole 1 is raisedvertically on the lateral side and on the medial side with the idea ofsupporting the foot by using support structures 157 and 158respectively. These structures give the medial upper arch an elastic andadjustable support. Thus, support structure 158 adds support shortlyafter heel strike e.g. in a case where the foot tends to pronate. Thesupport is achieved because the PU material of the midsole hassufficient mechanical strength to exert a stabilizing force. Inprinciple the support structure 158 could be made without window 159,but the supporting arm 155 has proved to give sufficient support.Additionally, structural element 160 has been added for furtherreinforcement. The vertical height of support structure 158 extends upto or above the upper half of the navicular bone 71 and medial cuneiformbone 72, and support structure 158 extends in longitudinal direction toapproximately the start of the first metatarsal phalanges.

Preferably, the support structures 158 and 157 are inclined inwardly tofollow the shape of the foot. As the support structures are anintegrated part of the midsole and thus made of polyurethane in thepreferred embodiment, the support structures have the same materialcharacteristics as PU and are thus able to keep the inclination duringuse and to exert a pressure against the upper 166 and the arch. Thelateral and medial support structures are bonded to the upper in apolyurethane injection process.

Toe end 36 (FIGS. 1a, 1b, 2a, 2b , 10, 11, 12 and 13) is likewise bondedto the upper in the injection process, and forms an integrated part ofthe midsole. The toe end is materially connected with the supportstructures 163 and 162 through a rim in the forefoot area, and isextended vertically from the base of the midsole 1 and curved inwardlyand pointing towards the heel. The design of this integrated toe capfollows the general inventive concept, namely to increase the supportingmaterial surface on the medial side as compared to the lateral side.Thus, as shown on FIG. 11, toe end 36 covers on its medial side an arealarger than on the lateral side as shown in FIG. 10. The extended toeend 36 is offset from a longitudinal centre line through the midsole tothe medial side, and stabilizes the foot during running and protects thetoes and the upper.

FIGS. 12 and 13 show an even further embodiment of a midsole 161provided with an upper 166. Support structures 162 and 163 are in thisembodiment made as a supporting mesh with openings 164 and 165. Lookingat the medial side in FIG. 12, sufficient structural support is ensuredby support arms 172 extending upwards to the lacing area 173 andcreating crossing sections 167, 172. The support structure 163 describesa structural mechanical stabilizing connection between the medial heelend and the medial forefoot, which ends in the upwardly extending toeend 36.

The described embodiments can be combined in different ways.

1.-14. (canceled)
 15. A sole for a running shoe for a foot of a wearerhaving cuneiform bones and a plurality of metatarsal phalanges, the solecomprising: a midsole having a heel portion, an arch portion, and aforefoot portion, the midsole having: a foot facing surface, and anoutsole facing surface including: a plurality of flex grooves thatextend into a material of the midsole, the plurality of flex groovescrossing each other and creating a plurality of discrete pads in themidsole, such that each pad is separated from other pads by at least oneflex groove, and a curved forefoot flex groove extending into thematerial of the midsole in a direction towards the foot facing surface,the curved forefoot flex groove having a first terminal end on a medialside of the arch portion and being oriented such that, when the weareris wearing a shoe with the sole, the curved forefoot flex groove followsan uninterrupted path towards the forefoot portion over one or more ofthe cuneiform bones and continuing between a third metatarsal phalangeand a fourth metatarsal phalange of the wearer, thereby providing anincreased flexibility in the forefoot portion of the shoe, and thecurved forefoot flex groove being further oriented to continue towards asecond terminal end in the forefoot portion; and an outsole including aplurality of discrete outsole elements separated from each other by atleast one flex groove, wherein the plurality of discrete pads in themidsole and the plurality of discrete outsole elements are arranged tofollow a spiral curve and arranged to be adjacent to the curved forefootflex groove.
 16. The sole according to claim 15, wherein the curvedforefoot flex groove is continued from a start of proximal phalangesover a third proximal phalange and is continued between a firstmetatarsal phalange and a second metatarsal phalange in a directiontowards the heel portion.
 17. The sole according to claim 16, whereinthe curved forefoot flex groove has a straight portion in the archportion and runs parallel to a straight reinforcement bar in themidsole.
 18. The sole according to claim 16, wherein the heel portion ofthe midsole has a curved heel flex groove emanating from a medial sideof the heel and stretching to a lateral side of the heel portion. 19.The sole according to claim 18, wherein the plurality of discreteoutsole elements are directly attached to respective midsole pads. 20.The sole according to claim 18, wherein the curved heel flex groove isbetween 1.5 and 3 times wider than the plurality of flex grooves,respectively.
 21. The sole according to claim 18, wherein the curvedheel flex groove has a depth of more than 50 percent of a thickness ofthe heel portion.
 22. The sole according to claim 15, wherein theforefoot portion of the midsole in a transverse direction from a medialside thereof towards a lateral side thereof includes at least a firstadditional flex groove following a path along the joints between theplurality of metatarsal phalanges and a plurality of proximal phalangesand crossing the curved forefoot flex groove.
 23. The sole according toclaim 22, wherein the forefoot portion of the midsole includes a secondadditional flex groove which follows a path along joints between theplurality of proximal phalanges and a plurality of medial phalanges,respectively.
 24. The sole according to claim 15, wherein the curvedforefoot flex groove runs in a longitudinal direction from the medialside of the arch portion to an apex point in a metatarsal zone of thefoot.
 25. The sole according to claim 21, wherein the curved forefootflex groove continues in an opposite direction from the apex point in adirection facing the heel portion of the midsole.
 26. The sole accordingto claim 15, wherein the midsole is injection-molded and bonded on thefoot facing surface with an upper and on the outsole facing surface withthe plurality of discrete outsole elements.
 27. The sole according toclaim 15, wherein a shank is placed in or on the midsole, which shankextends in a longitudinal direction into a medial forefoot region and/ora lateral forefoot region.
 28. The sole according to claim 15, whereinan intermediate flexible layer of thermoplastic polyurethane (TPU) isplaced between the plurality of discrete outsole elements and themidsole, the intermediate flexible layer being between 0.5 and 2millimeters thick and following a shape of the plurality of flex groovesand the plurality of discrete pads of the midsole.
 29. The soleaccording to claim 15, wherein the plurality of discrete pads of themidsole have a larger surface area than the plurality of discreteoutsole elements.
 30. The sole according to claim 15, wherein the curvedforefoot flex groove has a width corresponding to between one and twotimes a distance between the third metatarsal phalange and the fourthmetatarsal phalange.